(1) Field of the Invention
The present invention relates to a key operation device for detecting the open/close state of each of a plurality of key switches through row and column signal lines coupled to form a matrix. The present invention also relates to a mobile terminal device having the key operation device.
(2) Description of the Related Art
Conventionally, compact mobile terminal devices, such as mobile phones, employ a key operation unit having a key matrix configuration composed of key scan lines and key sense lines.
The following describes a typical key matrix configuration, with reference to FIG. 8.
FIG. 8 shows the configuration of a key operation unit employed in a mobile phone.
As shown in FIG. 8, a conventional key matrix 10 is composed of five key scan lines (KeyScan 0-4) and five key sense lines (KeySense 0-4). A plurality of switches that correspond one-to-one with a plurality of keys of the mobile phone (not shown) are coupled to the key scan lines.
FIG. 9 is a diagram showing the allocation of the keys on the key matrix 10.
The key matrix 10 is coupled to a key scan circuit 11 having a plurality of input/output ports. More specifically, the key scan lines are coupled to the output ports, whereas the key sense lines are coupled to the input ports.
A key sense pull-up circuit 12 having resistors R0-R4 is coupled to the respective key sense lines, so that the output signal of each key sense line is pulled up to a high level at all times when the corresponding switch is open. The key scan circuit 11 sequentially outputs low-level signals to scan the key scanlines and detects the open/close state of each key switch.
Suppose, for example, that a key scan signal is output to KeyScan 0 during the time “TALK” Key is pressed. Under this state, the key switch corresponding to “TALK” Key is closed and thus KeySense 2 is brought into conduction with KeyScan 0. Consequently, the key scan signal output to KeyScan 0 pulls the output signal of KeySense 2 down to a low level. Based on this change in signal level, it is detected that “TALK” Key is pressed.
Recently developed mobile phones are capable of executing game applications thereon. With such a mobile phone, users can play a game by manipulating keys on the key operation unit.
Generally, such a newly-developed mobile phone has a key operation unit that includes a cross-key pad composed of up, down, left, and right keys for input of the respective directions, and also includes numeric keys and symbol keys (i.e., “*” Key and “#” Key). The respective keys are associated with specific functions for playing the game.
During the game, the user may press “↑” and “→” Keys of the cross-key pad at the same time to move a character presented on a display screen in an oblique (up and right) direction. Additionally, the user may press “1” Key of the ten-key pad simultaneously with “↑” and “→” Keys. As above, it often happens during the game that a complex combination of two or more keys of are simultaneously pressed, although such simultaneous key pressing is not normally expected during the time the mobile phone is used to execute phone functions.
Unfortunately, however, the key operation unit having the above-described conventional key matrix configuration may not be able to properly respond to simultaneous pressing of two keys of the cross-key pad when another key of the ten-key pad is also pressed simultaneously.
The malfunction noted above is described with reference to FIGS. 9 and 10.
In the figures, the up, down, left, and right keys are denoted simply as “↑”, “↓”, “←”, “→” and respectively. Thus, also in the description, the up, down, left, and right keys may be denoted as “↑”, “↓”, “←”, and “→” Keys, respectively.
For purposes of description, it is supposed that “↑” and “→” Keys as well as “1” Key are simultaneously pressed. When the key scan circuit 11 scans KeyScan 1 under this state, both KeySense 0 and KeySense 2 are brought into conduction with KeyScan 1. As a result, it is detected that “→” and “1” Keys are pressed.
When the key scan circuit 11 subsequently scans KeyScan 3, KeySense 2 is brought into conduction with KeyScan 3. As a result, it is detected that “↑” Key is pressed. It should be noted, however, that KeySense 0 is also brought into conduction with KeyScan 3 as shown in FIG. 9 because the key switches corresponding to “↑”, “→” and “1” Keys are closed.
As a result of this unintentional conduction, the key scan circuit 11 erroneously detects that “7” Key is also pressed although the key is not pressed. With such malfunctions, it is no longer ensured that the user can correctly play games using the cross-key pad and ten-key pad.
Each key of the ten-key pad other than “7” Key also involves a similar risk as long as the key is coupled to one of the two key scan lines and to one of the two key sense lines that are used to detect pressing of the up, down, left, and right keys. The up, down, left, and right keys are likely to be pressed at the same time.
For example, when “↑” and “→” Keys are simultaneously pressed, an additional key press of any of “1”, “2”, “3”, “7”, “8”, and “9” Keys may cause an erroneous detection. On the other hand, when “↑” and “←” Keys are simultaneously pressed, an additional key press of any of “4”, “5”, “6”, “7”, “8”, and “9” may cause an erroneous detection. When “↓” and “→” Keys are simultaneously pressed, an additional key press of any of “1”, “2”, “3”, “*”, “0”, and “#” may cause an erroneous detection. When “↓” and “←” Keys are simultaneously pressed, an additional key press of any of “4”, “5”, “5”, “6”, “*”, “0”, and “#” may cause an erroneous detection.
As described above, the conventional key matrix as shown in FIG. 7 fails to correctly handle the key operation of simultaneous pressing of two directional keys to make an oblique-direction movement, if any key of the ten-key pad is additionally pressed simultaneously with the two directional keys.
The above problem is solved by coupling a rectifier circuit (diode) to each key switch as shown FIG. 11 to prevent reverse-current. Yet, this solution is not preferable in view of additional cost required to provide a plurality of diodes. This solution is not preferable also in view of increase in the size of the key matrix due to space required to accommodate the diodes. This contradicts the desire to reduce the overall size of the mobile phone.